Reactive and Nonreactive Metals

• Copper, aluminum, iron and nonstainless steel react with acidic foods and release metals that can be toxic. These traces of metal can also change the taste of food, giving it a tinny, metallic flavor. The longer you store tomatoes in a copper vessel, the more metal they will absorb. Fortunately, food storage containers are rarely made from these reactive metals. It is unlikely that you will store cooked tomatoes or tomato sauce in copper unless you cook them in a copper pan, then put the pan in the refrigerator. Stainless steel and clay are nonreactive cooking materials in which you can safely store tomatoes.

Tomato Sauce

• Tomato sauce is usually made from cooked tomatoes, which have been chopped or pureed then reduced and seasoned. The process of reducing concentrates the acidity by cooking out moisture, leaving a higher ratio of acid to food. If possible, avoid storing tomato sauce in copper. If you have no other storage vessel, use tomato sauce stored in copper as soon as possible or transfer it to a nonreactive container as soon as one is available.

Whole and Sliced Tomatoes

• Fresh whole tomatoes may be stored in a copper vessel such as a bowl or canister because the skins separates the acidic flesh from the reactive metal. For maximum safety, however, rinse whole tomatoes that have been stored in copper before using, even if you already rinsed them before you stored them. If the skin of any of your whole tomatoes breaks and the juice oozes onto the copper, discard the damaged tomato as well as any others that have come into contact with its juice. If possible, avoid storing sliced tomatoes in copper because their juice will leak and react with the metal.

Copper Food Storage Benefits

• Storing food in copper impedes the spread of food-borne microbes. It takes 4 hours for E. coli bacteria to die after coming into contact with a copper surface, while it takes 34 days for the pathogen to die on a stainless steel surface. Despite this benefit, copper can still cause digestive issues when it leeches out into tomatoes, so it's best not to use it for storing them.